Copending application Ser. No. 681,438, filed Apr. 29, 1976, now U.S. Pat. No. 4,028,647, in the name of H. K. H. Yee as inventor, discloses an improved monolithic piezoelectric filter unit having two bilateral electrodes on one surface and a common electrode on the opposite surface with the common electrode connected to the common terminal of the filter unit via a capacitor (C.sub.c). The latter, in cooperation with the coupling between the two bilateral electrodes, introduces a pair of finite poles one in each of the upper and the lower stopbands on either side of the passband of the filter unit. An advantage of such arrangement is that the tolerance on the internal coupling coefficient of the monolithic crystal may be relaxed.
In utilizing monolithic crystals to realize Single Side Band (SSB) filters, it is advantageous to have all finite poles in either of the upper or lower stopbands exclusively, depending on which sideband is involved.